.nav{
    width:100%;
    height:.8rem;
    border-bottom: 1px solid #999;
    text-align: center;
    background-color: #fff;
}
.nav a{
    font-size:.3rem;
    display: block;
    width:33.33%;
    text-align: center;
    color:#000;
    height:.8rem;
    line-height: .8rem;
    float: left;
}
.nav a span{
    padding-bottom:.16rem;
}
.nav a.active{
    color:#f00;
}
.nav a.active span{
    color:#f00;
    border-bottom: 3px solid #f00;
}